Radioimmunoassay of creatine kinase isoenzymes in human serum: isoenzyme BB.

We describe a sensitive, specific radioimmunoassay for the BB isoenzyme of creatine kinase (CK-BB) in serum. A sequential saturation assay was used to achieve sufficient sensitivity to detect the isoenzyme in 100-microliter serum samples of all healthy persons and patients tested. Bound and free antigen were separated by a second antibody system. Large excesses of purified isoenzyme MM did not react in the assay. Cross reactivity of two preparations of CK-MB was only 1 to 7+. The 95th percentile of serum CK-BB in 208 healthy adults was 6.2 microgram/liter. Within-assay and between-assay precision ranged from 5.5 to 11.9% and 9.7 to 13.6%, respectively.